Feline upper respiratory infection, known as URI, is a highly contagious viral infection that is particularly prevalent in animal and rescue shelters and catteries. Feline herpes and calicivirus account for 80 to 90 percent of feline URI cases and do not respond to antibiotics. However, in some cases, secondary bacterial infections, such as chlamydophila, mycoplasma and bordetella, may also be present (either causing the URI or running concurrently with the viral infection) and UC Davis recommends antibiotic therapy as part of the treatment regimen.
Amoxicillin is derived from penicillin. Potassium clavulanate is added to increase amoxicillin's bacteria-killing power by protecting it against certain bacteria types that destroy penicillin; the resulting combination is a powerful antibiotic that is commonly prescribed for feline URI. Side effects of amoxicillin/clavulanate include nausea and vomiting (which may be reduced by administering the medication with food), diarrhea, drooling and, in rare cases, liver damage signified by jaundice. Felines allergic to penicillin should not be given amoxicillin.
Cephalosporins are also derived from bacteria and are classified into three separate groups. The first group, or first generation cephalosporins, are the most effective in treating feline URI, according to UC Davis and Mar Vista Animal Medical Center. These medications are available in "gummie chew" and liquid form and side effects are considered rare. Should they occur, however, they include decreased appetite, nausea and vomiting, diarrhea, rashes and high fevers. Cats allergic to penicillin should avoid cephalosporin antibiotics.
Doxycycline is a member of the tetracycline family and is effective by "inhibiting bacterial protein synthesis," reports Mar Vista Animal Medical Center. Doxycycline is capable of penetrating the body's natural protective barriers into the cells, making it an effective treatment against Chlamydophila felis, a cellular bacterial inhabitant of some feline URI cases. Side effects of doxycycline include nausea and vomiting, photosensitivity, stained teeth in kittens ,and rashes, facial swelling or other signs of allergic reaction. Doctors Foster and Smith warn that cats must be given 1 tsp. of water with doxycycline pills to prevent esophageal damage.